Ultra-high voltage devices only can use self-protection scheme since they are often huge dimension devices. ESD protection schemes, increasing the dimensions of some critical layouts, are not available for Ultra-high voltage devices since they are already huge dimension devices. Even the dimension of ultra-high voltage devices is very huge, they still cannot meet the minimum ESD requirement. The root cause is that the device is non-uniform triggering on to induce the current localized at a finite region. Typically, a conventional ultra-high voltage device has a vertical cross-sectional view as shown in FIG. 1, in which a P-substrate 10 has a P-epilayer 12 thereon, a P-well 14 and a high voltage N-well 16 are formed on the P-epilayer 12, the high voltage N-well 16 has an oxide 28 thereon, and a contact region 18 is formed by doping the surface of the high voltage N-well 16 through an opening not covered by the oxide 28, and is electrically connected to a high voltage electrode HV through a contact plug 20, a first metal layer 22, a via 26 and a second metal layer 24, which is the high voltage path of the ultra-high voltage device. The high voltage N-well 16 raises the breakdown voltage of the ultra-high voltage device, thereby allowing the device to support high voltage operation. In FIG. 2, the drawing in the upper part is a layout of the ultra-high voltage device shown in FIG. 1, the lower drawing is an enlarged view of the area 30 in the foregoing layout. The contact plug 20 has a stripe shape in the horizontal cross-section of the ultra-high voltage device, and the terminal 32 of the contact region 18 is often the non-uniform portion of the ultra-high voltage device. When there is a great current, such as an ESD current, flowing through the high voltage path, the current intends to concentrate around the terminal 32 and produce great heat, resulting in localized high temperature to melt down this portion of the ultra-high voltage device. Once any portion of the high voltage path is burnt down, the ultra-high voltage device will lose its high voltage withstanding capability and become no more usable.
To date, there has not been any ESD protection about the ultra-high voltage technology, typically referring to the voltage equal to or higher than 500V, and thus an ultra-high voltage device only can be protected by its structure itself.